Melting and casting apparatus



Oct. 25, 1955 w. J. TRETHEWAY ET AL 2,721,364

MELTING AND CASTING APPARATUS 2 Sheets-Sheet 1 Filed Oct. 12, 1951 44 Jwk Oct. 25, 1955 w TRETHEWAY ET AL 2,721,364

MELTING AND CASTING APPARATUS Filed Oct. 12, 1951. 2 Sheets-Sheet 2 FIG.3 1

United States Patent MELTING AND CASTING APPARATUS William J. Tretheway,Laguna Beach, Calif., and Rollin J. Kennard, Butte, and Earl L. Buker,Great Falls, Mont., assignors to The Anaconda Company, a corporation ofMontana Application October 12, 1951, Serial No. 251,024

2 Claims. (CI. 22-79) This invention relates to melting and castingcadmium metal, and more particularly is concerned with the provision ofimproved apparatus for melting metallic cadmium and delivering it to amold.

A difficulty commonly encountered in casting cadmium metal is inpreventing it from oxidizing, especially after removal from the meltingfurnace and during delivery to a casting apparatus or mold. Unless thisdifficulty is overcome and oxidation of the molten cadmium issubstantially prevented, castings made therefrom are likely to containdross inclusions. Another difiiculty encountered in producing densecastings of cadmium is in delivering the molten metal to the castingapparatus or mold rapidly and at a controlled temperature. Unlesscadmium is cast at the optimum temperature, the castings are apt to beobjectionably porous, as well as undesirably rough at their surfaces.

In the past, withdrawal of cadmium from a melting furnace and pouringinto molds has been primarily a hand operation, and as such has not, asa rule, satisfactorily met the aforementioned requirements of avoidingoxidation and casting at the optimum temperature. It is the primaryobject of this invention to provide improved apparatus for preparingcadmium for casting and delivering it to a casting apparatus or moldmechanically, so that such requirements are met.

Apparatus according to the invention for preparing and delivering moltencadmium to a casting apparatus or mold comprises a furnace, including amelting pot, and means for heating the melting pot evenly and to quiteaccurately controlled temperatures. Advantageously the heating means ofthe furnace comprises a plurality of gas burners adapted to supply heatto the pot by an encircling flame, an exhaust fan being employed toexhaust the combustion gases from the bottom of the furnace, thereby toheat the bottom of the pot evenly.

One or more delivery pipes is removably secured to the bottom of the potand extends therefrom to a point closely adjacent the entrance or mouthof a mold. The

delivery pipe or pipes are advantageously well insulated substantiallythroughout their length. Electrical heating means are provided tomaintain the molten metal in the pipes, after it has been withdrawn fromthe pot and until it is discharged into a mold, at an optimum castingtemperature. Such electrical heating means advantageously comprises astep-down transformer supplied with current from a convenient powersource. The terminals of the low voltage secondary of the transformerare electrically connected by suitable conductors to the extremeopposite ends of the delivery pipe whereby the delivery pipe and themetal therein may be supplied with a low voltage heating current ofadequate amperage. It is particularly advantageous, in order to controlthe temperature of the molten metal in the delivery pipe most accuratelyand economically, for the conductors bywhich the low voltage secondaryis connected to the delivery pipe to be of metal of good electricalconductivity throughout a substantial part of their length, but for theend portions of such conductors, which are connected to the ends of thepipe, to be of metal of high electrical resistance and poor thermalconductivity, e. g. stainless steel. Where a number of delivery pipesare all connected to the same pot, a number of transformers areemployed, one terminal of the low voltage secondary of each beingelectrically connected to the outer end of a delivery pipe. The otherterminals of the low voltage secondaries of the transformers areelectrically connected together and to the melting pot. By these meansthe molten metal may at all times be maintained at the desiredtemperature until it is actually discharged into a mold.

Another very important feature of the invention resides in the provisionof means at the outer end of each delivery pipe whereby the deliverypipes are always maintained substantially full of cadmium metal. Suchmeans comprises a gooseneck section including a vertically upstandingportion, mounted on each delivery pipe at its outer end. The main run ofthe delivery pipe is substantially horizontal, and the verticallyupstanding portion prevents partial emptying of the delivery pipe whenthe molten metal is shut off by a valve located, say, near the meltingpot. The outer portion of the gooseneck section is removable from thedelivery pipe at a point adjacent the highest point of the verticallyupstanding portion thereof. The removable portion is advantageouslyformed with a spout which serves to convey the molten metal to a pointclosely adjacent the mold face; and because it is removable it may bereadily and easily kept clean and free of dross.

For a more detailed understanding of the method and apparatus of ourinvention, reference may be made to the accompanying drawings in whichFig. 1 is a plan view of the new cadmium melting furnace and itscombustion gas exhaust system;

Fig. 2 is a sectional elevation of the apparatus of Fig. 1 taken alongline 2-2 thereof;

Fig. 3 is an elevation, partially diagrammatic and partially in phantom,illustrating the cadmium metal delivery system and the electricalheating means therefor;

Fig. 4 is an enlarged sectional view of a section of the furnaceillustrating the disposition of one gas burner;

Fig. 5 is an enlarged partial section on line 55 of Fig. 1;

Fig. 6 is a sectional view of the pot end of one delivery pipe and themeans for supplying electric current to the pot and the pipe; and

Fig. 7 is an enlarged perspective view showing a removable gooseneck atthe discharge end of a delivery pipe for molten metal.

The gas fired cadmium melting furnace, best shown in Figs. 1 and 2,comprises a furnace shell 10 suitably lined with fire brick 11 andhaving an opening 12 located centrally in the bottom thereof fordowndraft exhaust of the combustion gasesv A steel melting pot 13 havinga peripheral rim flange 14 is hung centrally by such flange in thefurnace. The bottom of the pot is provided with a sump 15 to which areremovably secured delivery pipes 16 and 17 for transferring molten metalto molds.

A plurality of valve blocks 18 (see Fig. 5), one for each delivery pipe,are mounted in the bottom of the sump 15, and each is provided with avalve seat 19. A poppet-type valve closure element 2% is provided foreach valve block 18, and when lowered into engagement with valve seat 19the closure element halts the flow of molten metal from the pot 13 intoand through the corresponding delivery pipe. The valve element 20 issupported at the lower-end of a rod 21 which extends upwardly within thepot 13 and is pivotally connected at its upper end to a bell crank plate22 (Fig. 2). The plate 22 is pivotally supported on a mounting bracket23 which is in turn supported on the top of the lined furnace shelladjacent the rim or flange 14 of the pot 13. The plate 22 is alsopivotally connected to one end of a threaded rod 24, the opposite end ofwhich is provided with a handle 25 by which it may be turned. Thethreaded rod 24 passes through a threaded nut 26 which is secured to themounting bracket 23. To close a poppet valve in the sump of pot 13, inorder to prevent the flow of molten metal from the pot, the threaded rod24 is turned by its handle to pivot the bell crank plate 22 in aclockwise direction, as seen in Fig. 2. To open the poppet valve thethreaded rod 24 is turned in the opposite direction. A separate poppetvalve is advantageously provided to control the flow of molten metalfrom the pot through each separate delivery pipe; and each poppet valveadvantageously is provided with an individual opening and closingapparatus of the character described.

As has been previously pointed out, cadmium metal oxidizes so readilythat extreme care must be taken in heating it for casting. When a gasflame is to be employed for heating the melting pot, therefore, theflame should be very carefully controlled to provide a well distributedheating of the pot, in order to avoid development of hot spots in themolten metal. To assure even distribution of heat to the melting pot 13,a plurality of gas burners, each indicated generally by the numeral 30(Fig. l), are provided. These gas burners are all supplied with afuel-air mixture from a common source through an inlet nozzle 31 securedtangentially to a bustle pipe 32 to which each gas burner 30 isconnected by an individual feed pipe 33. As may best be seen in Fig. 4,the feed pipe 33 for the gas burner leads into a chamber 34 provided atthe apex of a conically shaped member 35. A nozzle passage 36, arrangedto direct a flame substantially tangentially into the combustion areabetween the inner face of the furnace lining 11 and the outer surface ofmelting pot 13, extends angularly from the chamber 34. Auxiliarycombustion air enters the nozzle passage 36 through a passage 37 whichopens to the atmosphere at the furnace wall. This passage also forms apeep hole or window by which one can observe if the burner is ignited.In the furnace as described, when the burners are in operation, theflame within the combustion area of the furnace will be given a whirlingmotion around the pot by reason of the arrangement of burner nozzles 36.The pot will, therefore, be subjected to substantially uniform heatingall about its periphery.

In order to assure even heating of the bottom as well as the sides ofthe melting pot 13, an exhaust fan 40, capable of withstanding hightemperature gases, is provided to withdraw the combustion gases from thebottom of the furnace combustion area through the bottom opening 12 andthence through a flue 41 lined with a refractory material 42. Theexhaust fan discharges the combustion gases to the atmosphere through astack 43. Such downdrafting of the melting furnace insures that thebottom of the melting pot 13, as well as its sides, is evenly heated.

More or less conventional temperature controls (not shown) areadvantageously employed to control the temperature of the metal in themelting pot 13 during melting of the cadmium, and for maintaining it atthe desired temperature during a casting operation. When cadmium ismelted in the above-described furnace, the exposed surface of the moltencadmium in the pot 13 is protected by a fused layer of caustic (sodiumhydroxide) to prevent oxidation of the metal and formation of dross. Byremoving the molten metal from the bottom of the pot only, through thesump 15, none of the caustic or other material floating on the surfaceof the molten metal is included in it.

The particular construction of the molten metal delivery pipes 16 and 17and of the electrical heating means therefor are illustrated in Figs. 3,6 and 7. The delivery pipe 16, preferably made of stainless steel, is 7threaded into a stainless steel bushing or coupling 44 which in turn isthreaded into a steel plate 45 welded to the outer face of the sump 15of the melting pot 13. The delivery pipe 16 is insulated substantiallythroughout its length with an insulating material 46 adapted towithstand temperatures up to, say, 1000 F. This delivery pipe isprovided for supplying molten cadmium from the furnace to a ball moldcasting apparatus 47 illustrated in phantom. This casting apparatusforms no part of the present invention, but an advantageous form of suchapparatus is disclosed and claimed in our copending application SerialNo. 246,272, filed September 12, 1951, now Patent No. 2,689,989.

Over most of its run the delivery pipe 16 is substantially horizontal,but its outer end portion is bent to form a vertically upstandingsection 48 which effectively serves to maintain the delivery pipe fullof molten metal at all times. The upstanding section 48 forms the innerportion of a gooseneck 49 at the end of the delivery pipe. The outerportion 50 of the gooseneck is removably attached to the inner portion,at a point adjacent the highest point of the gooseneck, by matingcoupling members 51 and 52 which are secured together by screws 53. Thelower end of the outer gooseneck portion 50 is formed with a spout 54adapted to be located closely adjacent the entrance to the mold of thecasting apparatus 47, whereby molten metal removed from the furnace potfor delivery to the mold of the casting apparatus is exposed to anoxidizing atmosphere for but a very brief instant prior to entry intothe mold. If desired, an atmosphere of carbon dioxide or othersubstantially non-oxidizing gas may be maintained within the castingapparatus 47. The outer portion 50 of the gooseneck advantageously isremoved at the end of each cycle of casting operations, for cleaning andremoval of any dross that has accumulated therein. The upstanding innerportion 48 of the gooseneck serves to maintain the delivery pipe 16 fullof molten metal at all times, whereby the interior of the delivery pipeis kept free of dross.

As shown in Fig. 3, an additional valve 55 is advantageously connectedinto delivery pipe 16 to control the flow of molten metal therethrough.This valve is adapted to be automatically operated, to turn the flow ofmolten cadmium on and ofl in proper synchronism with operation of thecasting apparatus 47.

Electrical heating means for the delivery pipe 16 comprises a variablestep-down transformer the terminals of the high voltage primary 61 ofwhich are connected across power lines L1 and L2. The terminals of theloW voltage secondary 62 are electrically connected to a pair of copperpipe bus bars 63 and 64. One of these copper pipes 63 is connected tothe upstanding section 48 of the delivery pipe 16, as close as possibleto the end thereof, by a stainless steel connector having an outersection 65 which is welded or otherwise secured to the inner gooseneckportion 48 and having an inner section 66 of substantially greatercross-sectional area than the outer section which is clamped to thecopper pipe 63. The outer section 65 of the stainless steel connector,because of its reduced cross section, is of relatively high electricalresistance and hence is heated by the electrical current flowing throughit to a higher temperature than the inner section 66. Thereby it ismaintained at a temperature high enough to avoid undesirable cooling ofthe delivery pipe. Heat insulation may be used if desired to keep thetemperature of the outer section 65 adequately high. The inner section66, at least near the copper pipe 63, is uninsulated so that radiationof heat therefrom keeps the temperature at the clamp low enough to avoidoxidation of the copper and damage to the electrical connection.Stainless steel is preferred 'for making the connector 65, 66 because itdoes not oxidize and scale at the high temperature to which it issubjected; and also the low heat conductivity of stainless steelminimizes the loss of heat by conduction to the (cold copper pipe bus63.

The other copper :bus bar pipe '64 is electrically connected at itslower end to the steel plate 45 on the melting pot 13 by a connectorcomprising a pair of stainless steel clamps 67 and 68 joined together bya stainless steel bar 69 and a stainless steel pipe 70. The clamp .67 issecured to the copper pipe 64, while the clamp 68 is secured to theouter end of the stainless steel pipe 70. The latter is concentric withand surrounds the inner end of the delivery pipe 16 but is separatedfrom the delivery pipe by the insulation 46. The inner end of thestainless steel pipe '78 is welded to the stainless steel bushing 44(Fig. 6) which, as has been explained, is screw-threaded to the steelplate 45. The delivery pipe 16 and the stainless steel pipe 70 both passthrough the same hole in the furnace shell without either touching it orincluding any part of the iron shell within a conducting loop, forotherwise its magnetic character would cause heating of the shell andloss of power thereby. The stainless steel from which sections 65 and 66of the conductor leading to the outer end of the delivery pipe and bar69 and pipe 70 leading to the melting pots may be made may be, forexample, one consisting of 18% chromium, 8% nickel, 2% molybdenum as thestabilizer and the balance iron with the insignificant amounts ofimpurities. The thermal conductivity of such stainless steel at 400 C.is 0.048 calorie per square centimeter per centimeter per degreeCentigrade per second.

The electrical circuit for heating the metal in delivery pipe 16 andthereby maintaining it molten, therefore, comprises the low voltagesecondary 62 of the variable transformer 60, the copper bus bar pipe 63connected to one terminal of the secondary 62, the stainless steelconnector 66, 65, the delivery pipe 16 and the metal therein, thebushing 44, the stainless steel pipe 70, the stainless steel clamps 68and 67 and their connecting bar 69, and the copper bus bar pipe 64 whichis connected to the other terminal of the low voltage secondary 62 ofthe variable transformer.

The apparatus shown in the drawings is provided with the second deliverypipe 17, generally similar to the delivery pipe 16 described above, fordelivering molten cadmium to a different set of molds than those of thecasting apparatus 47. The delivery pipe 17 is advantageously composed ofstainless steel and is insulated substantially throughout its lengthwith a material 71 similar to that used for insulating the delivery pipe16. As previously described, the delivery pipe 17 is removably securedto the sump of the melting pot 13, and at least one valve 72 is providedto control the fiow of molten metal through it. While in Fig. 3 thedelivery pipe 17 is shown, for reasons of convenience, as being ofsomewhat lesser length than is the delivery pipe 16, in practice it maybe longer than the latter. At its outer end the delivery pipe 17 isprovided with a gooseneck 75 of the same character as the gooseneck 49.The delivery pipe 17, like the corresponding pipe 16, is adapted to beheated electrically. To this end, a second variable stepdown transformer80 is provided having a high voltage primary 81 connected to the powerlines L1 and L2. The low voltage secondary 82 of the transformer 80 hasits terminals electrically connected to a pair of copper bus bar pipes83 and 84. One of these pipes 83 is directly connected to the copperpipe 64 which is in turn connected to the melting pot. The other ofthese copper pipes 84 is electrically connected to the upstanding innersection of the gooseneck 75 by a stainless steel connecting clamp 86.The normal electrical heating circuit for the delivery pipe 17 thus isthe low voltage secondary 82 of the transformer 80, the copper pipes 83and 64, the stainless steel clamps 67 and 68 and their connecting bar69, the stainless steel pipe 70, the melting pot 13, the delivery pipe17 itself and the molten metal contained therein, the flexible laminatedstainless steel connecting clamp 86, and the copper pipe 84.

By the above-described electrical heating means the delivery pipes andthe metal contained therein may be subjected to the heating action of alow voltage current of adequate amperage to maintain the temperature ofthe molten cadmium in the pipes at the optimum casting temperature, withminimum loss of heat to the cold conductors of the heating circuit.

In order that either or both of the delivery pipes 16 and 17 may beemployed if and when the stainless steel pipe is disconnected from thepot 13 for repair or for any other reason, an auxiliary or emergencyelectrical connection between the copper pipe 64 and the melting pot 13is provided. This auxiliary electrical connection comprises a steel bar90 welded to the flange 14 of the steel melting pot 13, a stainlesssteel bar 91 secured thereto by a stainless steel connecting member 92,and a stainless steel clamp 93 and connection member 94, the formerbeing connected to the copper pipe 64 and the latter to the stainlesssteel bar 91.

In using the above-described apparatus for preparing cadmium metal forcasting and for delivering the molten metal to a casting apparatus ofthe type described in our aforementioned application Serial No. 246,272,now Patent No. 2,689,989 the molten metal should be supplied to theentrance to the mold of the casting apparatus without substantialexposure to an oxidizing atmosphere (such is substantially prevented bythe design of the apparatus) and at a temperature of about 700 to 800F., preferably 760 F. A higher casting temperature results in excessivetime being required for the castings to cool and solidify, thus slowingup the casting operation, and a lower casting temperature results inrough castings. To assure delivery of the metal to the mold at thecorrect temperature, the cadmium in the melting pot 13, after beingmelted, should be held at a temperature in the range from 800 to 900 F.,and best at about 850 F. If the temperature of the molten metal in thepot is lower, the flow of metal through the delivery pipe may be toorapid for the electrical heating system to maintain it at the desiredtemperature. On the other hand, if the metal in the pot is substantiallyhigher, it may not cool off to the correct value in sufiicient time tobe delivered to the mold of the casting apparatus at the propertemperature. While in order to rapidly melt cadmium supplied to thefurnace and pot, the pot may be heated to a temperature of 900 F. to1000 F., preferably about 950 F., the temperature of the molten cadmiumshould therefore be decreased and maintained at about 850 F. during thecasting operation.

At the conclusion of a casting cycle, the valves 55 and 72 in thedelivery pipes 16 and 17 are closed, thereby shutting off the flow ofmetal from the melting pot into the delivery pipes; and the outerportions of the gooseneck sections 49 and are removed and cleaned. Thevertically upstanding inner portions of the gooseneck sections preventthe molten metal from draining from the delivery pipes when the valvesare closed, and keep the pipes full of cadmium at all times. The cadmiumin the delivery pipes advantageously is kept from solidifying bymaintaining the flow of heating current therethrough at all times. Thecadmium in the pipes meanwhile is fully protected against oxidationexcept at the tiny surface exposed in the vertical gooseneck section.

It is to be noted that for the purpose of remelting the metal in thedelivery pipe electrically, it is important that no cadmium has drainedtherefrom. Otherwise there will be substantial overheating and drossingof the cadmium in that part of the pipe from which the metal hasdrained.

We claim:

1. In apparatus for melting cadmium and delivering it to a moldincluding a melting pot and means for substantially evenly heating themelting pot, the improvement which comprises a delivery pipe secured tothe bottom of the pot and extending therefrom subtsantially horizontallyto the mold entrance, the delivery pipe having at its outer end asubstantially vertically upstanding portion forming part of a gooseneck,a power source, a stepdown transformer the high voltage primary of whichis connected to the powersource, and a pair of conductors connectedrespectively to the terminals of the low voltage secondary of thetransformer, one of said conductors being electrically connected to theouter end of the delivery pipe at the upper end of said verticallyupstanding portion thereof and the other conductor being electricallyconnected to said melting pot, the two conductors being made of metal ofgood electrical conductivity throughout substantial parts of theirlengths, both of said conductors, however, having their outer endportions which are connected to said upstanding portion of the deliverypipe and the melting pot respectively made of a metal of poor thermalconductivity.

2. Apparatus according to claim 1 in which a gooseneck section isremovably secured to the upper end of said vertically upstanding portionof the delivery pipe and forms the remainder of the gooseneck, thereversely curved portion of the gooseneck being a part of said goosenecksection, and in which the outer end portion of the conductor connectingthe low voltage secondary of the transformer to the substantiallyvertically upstanding portion of the delivery pipe has two sections, theone which is adjacent the end of the delivery pipe having a relativelyhigh electrical resistance whereby it is heated to a relatively hightemperature by an electrical current flowing therethrough.

References Cited in the file of this patent UNITED STATES PATENTS OTHERREFERENCES Page 8, Stainless Steels by Ernest E. Thum, The AmericanSociety for Metals, Cleveland, Ohio, second 7 edition, 1945.

' aids

1. IN APPARATUS FOR MELTING CADMIUM AND DELIVERING IT TO A MOLDINCLUDING A MELTING POT AND MEANS FOR SUBSTANTIALLY EVENLY HEATING THEMELTING POT, THE IMPROVEMENT WHICH COMPRISES A DELIVERY PIPE SECURED TOTHE BOTTOM OF THE POST AND EXTENDING THEREFROM SUBSTANTIALLYHORIZONTALLY TO THE MOLD ENTRANCE, THE DELIVERY PIPE HAVING AT ITS OUTEREND A SUBSTANTIALLY VERTICALLY UPSTANDING PORTION FORMING PART OF AGOOSENECK, A POWER SOURCE, A STEPDOWN TRANSFORMER THE HIGH VOLTAGEPRIMARY OF WHICH IS CONNECTED TO THE POWER SOURCE, AND A PAIR OFCONDUCTORS CONNECTED RESPECTIVELY TO THE TERMINALS OF THE LOW VOLTAGESECONDARY OF THE TRANSFORMER, ONE OF SAID CONDUCTORS BE-